The technical problems of video use control, such as video copy inhibition and copy control, are well known. These are techniques to prevent or discourage unauthorized copying of typically copyrighted movies or television programs or other video material. An example of copy inhibition is disclosed in Ryan U.S. Pat. No. 4,631,603 assignee Macrovision Corp. and incorporated herein by reference in its entirety, wherein an analog video signal is modified so that a television receiver will still provide a normal color picture from the modified video signal, while a video tape recording of the modified video signal when replayed produces generally unacceptable television pictures. This operates in the analog television domain. This “AGC” method relies on the fact that particular videocassette recorder (VCR) automatic gain control systems cannot distinguish between normal “sync” (synchronization) pulses of a conventional video signal and added “pseudo-sync” pulses. U.S. Pat. No. 4,631,603 discloses adding pseudo-sync (negative-going) pulses paired with positive-going (“automatic gain control”) pulses in the vertical blanking intervals of a television signal in order to result in unacceptable picture quality during playback of a recorded analog video signal.
Also well known are various copy control techniques suitable for use with either analog or digital video wherein a watermark or some other coded data is included in a video signal and is detected by an especially adapted video recorder. The video recorder upon detecting the watermark or coded data either permits or does not permit copying. In some cases, generational (e.g., copy once only) copy control is thereby provided.
The pseudo-sync and AGC-type pulses of U.S. Pat. No. 4,631,603 are shown here in FIGS. 1a and 1b, identical to FIGS. 1a and 1b of that patent where the horizontal scale is time and the vertical scale voltage, conventionally. The waveform of FIG. 1a illustrates a conventional video signal at a portion thereof having normal equalization pulses 10, but adapted in accordance with U.S. Pat. No. 4,631,603. The equalizing pulses are negative-going pulses which extend from the blanking reference signal level (marked on the vertical axis of FIG. 1a) down to the sync tip level (also marked on the vertical axis of FIG. 1a). In accordance with U.S. Pat. No. 4,631,603, a plurality of pulse pairs (e.g., adjacent pulses 12 and 14) are inserted after the equalizing pulse 10. As shown in accordance with NTSC television, a single tracing line or horizontal scan line for a television signal is approximately 63.55 microseconds in length as shown in FIG. 1a. Hence reference characters 12 of FIG. 1a illustrate the pseudo-sync pulses. Further each pseudo-sync pulse 12 is paired with an immediately following positive pulse 14. The positive pulses are also referred to as AGC or automatic gain control pulses since they affect the AGC circuit of a television receiver. In this case, the amplitude of the positive pulses is roughly equivalent to the amplitude of the peak white signal.
As stated above, the automatic gain control system of a typical videocassette recorder cannot distinguish between an equalizing pulse 10 and a pseudo-sync pulse 12 and therefore loses synchronization and hence loses proper recording signal reference level and fails to make an acceptable recording of the modified video signal.
FIG. 1b shows a waveform of U.S. Pat. No. 4,631,603 as applied to a horizontal scan line in the vertical blanking region having a normal horizontal synchronization pulse 16. This is followed by the conventional color burst information 18. In this case, seven pulse pairs of pseudo-sync pulses 12 and positive pulses 14 are inserted into the video signal after the sync pulse 16 and within the vertical blanking interval. The inclusion of seven such pairs in FIG. 1b is merely exemplary. Typically the positive or AGC pulses, as they are also known, have amplitudes extending to the clipping level of the medium through which the modified video signal must be transmitted. Typically this is between 100% and 125% of the peak white reference level. A typical duration of each of the AGC pulses 14 is 3 microseconds, although it may be shorter.
Also known is another copy protection technique also referred to as copy inhibition disclosed in Ryan U.S. Pat. No. 6,188,832, assignee Macrovision Corp. and incorporated herein by reference in its entirety. This discloses modifying a video signal so that a television/receiver still receives a normal picture from the modified signal whereas a video tape recording of this signal produces generally unacceptable pictures. This again exploits the automatic gain control circuitry in video tape recorders and their differences from the automatic gain control circuitry in television receivers and monitors. In this disclosure a portion of the back porch intervals following the trailing edges of a substantial number of horizontal sync pulses are significantly raised and lowered to improve the playability of the original signal without reducing the effectiveness of the copy protection of the copied signal. This is achieved by adding pulses to selected lines of the video signal during the back porch interval of horizontal blanking intervals. These pulses significantly raise or lower the voltage amplitude during the blanking interval so as to provide a signal for which the average voltage amplitude value is approximately equal to that of the blanking interval. This modification is typically made in a number of selected horizontal scan lines of the video signal typically clustered together and typically adjacent to a vertical blanking interval, in other words, near the end of the video field. However, this is not limiting.
FIG. 2 shows Ryan U.S. Pat. No. 6,188,832 FIG. 3 showing a portion of a waveform of a video signal modified in accordance with this back porch pulse copy protection technique. The waveform portion illustrated in present FIG. 2 is a portion of the video signal during the horizontal blanking interval. A positive pulse 26 has been added to the video signal immediately following the trailing edge of a horizontal sync pulse 22. For maximum effect, the amplitude of pulse 26 should be such as to raise the back porch voltage to a level of peak white or greater as shown in FIG. 2. A typical value of this positive pulse is 127 IRE units in the NTSC television format. The pulse width of the positive added pulse should be wide enough to overcome the limited video bandwidth of a typical recording video cassette recorder. This pulse is disclosed as being at least 750 nanoseconds in duration and is 1 microsecond in FIG. 2. Also shown in FIG. 2 are the conventional color burst 28 and the back porch video signal level at 24 and 30. The time durations of the various portions of this exemplary waveform are also indicated in microseconds in FIG. 2. Also disclosed in U.S. Pat. No. 6,188,832 is a typical circuit to generate such back porch pulse modification signals.
It is also known to use copy protection signals such as AGC pulses for purposes of controlling subsequent permitted use, such as storage or recording. See U.S. patent application Ser. No. 10/753,844 filed 7 Jan. 2004, published as WO2005/039176A1, inventor Mark A. HOLLAR, incorporated herein by reference in its entirety. This discloses a method and apparatus for controlling subsequent permitted use, such as storage, of video on a digital storage device, such as a personal video recorder. In this case, an analog video signal is provided with at least one modification to its video characteristics, for instance in the horizontal blanking interval and vertical blanking intervals, which is of the type having the capacity to inhibit making an acceptable analog of a recording of the analog signal. This is typically, for instance, the above-described AGC pulse addition or it may be the color stripe modification, also known in the field as developed by Macrovision Corp., see Ryan U.S. Pat. No. 4,577,216 and Wrobleski et al. U.S. Pat. No. 6,516,132, both incorporated herein by reference in their entirety. In the color stripe process, the color burst conventionally present in the horizontal blanking interval in each line of active video in the analog domain is modified in terms of its phase so that any subsequent video tape recording of the video signal shows undesirable variations in the color fidelity that appear as bands or stripes of color error.
WO2005/039176 uses the presence or absence of these types of copy inhibition modifications to serve as a type of code to carry information as to the subsequent permitted use in the digital realm, such as whether the accompanying content of the video signal is allowed to be digitally recorded in digital form, and if it is allowed to be recorded, also the length of time that the recording is allowed to persist. Hence in this case the modifications to the analog video signal have a dual use in both inhibiting recording in the analog realm and carrying information across the analog video interface so as to control storage (copying) or other use of the video in the digital realm.
In the disclosure of WO2005/039176, the copy inhibition processes are provided in a pattern used to carry data controlling uses of the video, such as a permitted subsequent digital storage of the video signal, for instance in a personal video recorder. In one embodiment, the AGC and color stripe processes are each present (on) or not present (off). Since there are two such processes each with two conditions (present or not), this provides four different states in one embodiment, in other words providing in effect a four bit digital value. Thus each state has a coded meaning in terms of copy control, for instance the first state indicates there is no copy control in storage, for instance in a PVR, as permitted with no limitation. The second state indicates storage is not permitted. The third state indicates that duration of storage in terms of, for instance, hours, days, etc. The fourth state indicates a storage is permitted, but of the specified duration only.
Also known in the television field is conveyance of information for an analog TV signal in the 21st line of a video field and the vertical blanking interval. For instance, close captioning and CGMS (copy generation restriction management system) impose what amount to digital signals in this particular scan line. However, it is noted that this particular line, in fact, is typically reserved, for instance, in NTSC television specifically for carrying close captioning and CGMS data. This is according to an FCC standard. Moreover, there is only one scan line provided for this per video field since it is in the vertical blanking interval and occupies the entire line. Hence not only is this a government mandated information conveyance approach it also has very restricted bandwidth in terms of how much information is carried per field. (A field in television is one-half a frame comprising the even or odd numbered lines in a frame; two such fields together make up a frame where there are 30 frames per second displayed in NTSC television.) The same general approach is used in other television systems which are SECAM and PAL with slightly different parameters. Such a system is described in Ezaki et al. U.S. Pat. No. 5,822,425.